1. Field of the Invention
The present invention relates to the production of high-analysis solution-type fertilizers, said fertilizer solutions being produced by the reaction of phosphoric acid with commercially available nitrogen solutions such as those containing 34 percent urea, 46 percent ammonium nitrate, and 20 percent water, with a specified amount of additional solid urea dissolved in such solutions. In the production of the instant, new, and novel high-analysis solutions, the typical grades produced thereby range from 24-12-0 or 25-11-0 to 30-4-0 and remain as clear solutions without any precipitation occurring therein for substantial periods of time at temperatures as low as 0.degree. C.
It now has been discovered that these high-analysis solutions, i.e., 35 percent TPN fertilizers, must have specific ratios maintained between the three main components: P.sub.2 O.sub.5, urea-nitrogen, and ammonium nitrate-nitrogen. For the sake of convenience to the reader, the urea (nitrogen) and/or the ammonium nitrate (nitrogen) may oftentimes hereinafter be simply referred to as urea-N or ammonium nitrate-N, respectively. Additionally, as noted supra, there must be maintained a specific range of weight ratios between the total phosphate values, expressed as P.sub.2 O.sub.5, and total nitrogen content of such solutions. Thusly, three separate but interactive or interrelated proportions or ratio ranges must be maintained, e.g., the required proportion of P.sub.2 O.sub.5 to total nitrogen for TPN of 35 percent is kept at a weight ratio of between 0.538 and 0.316 (about 0.3 to 0.5), the required proportion of urea-N to ammonium nitrate-N is kept between about 15:1 to about 4:1 (weight ratio ranging between about 15 and about 4), and the required proportion of urea-N to ammonium nitrate-N plus P.sub.2 O.sub.5 is kept between a weight ratio of about 1.24 to about 1.81 for 34 percent TPN (1.41 to 1.59 for 35 percent TPN).
2. Description of the Prior Art
Urea phosphoric acid adducts and their production have been known for over 60 years. In U.S. Pat. No. 1,440,056, Clarkson, et al., Dec. 26, 1922, teach a process for the production of urea phosphoric acid. In their process, urea was reacted with phosphoric acid thereby producing a urea phosphoric acid adduct. The resulting urea phosphoric acid adduct could be dissolved in water for the subsequent production of N-P type fertilizer solution, with the highest analysis solution thus obtained being 34.8 percent total nutrient content at 0.degree. C. for a singular point. [Kaganski, Z. M., Gordienko, V. M., "Mutual Solubility in the System CO(NH.sub.2).sub.2 --H.sub.3 PO.sub.4 --HNO.sub.3 --H.sub.2 O," Zhur. Prik. Khim. 40 (2), 284-90 (1967). Luff, B. B., Reed, R. B., "Enthalpies of Reaction of Phosphoric Acid Solutions and Urea at 25.degree. C.," J. Chem. Eng. Data 20 (4), 420-31 (1975). Nabier, M. N., et al., "Solubility of Ternary and Quaternary Systems of Urea Nitrate and Some Components of Mineral Fertilizers," Uzbek. Khim. Zhur. 6, 3-9 (1980). Narathmetor, N. N., Berenzhanov, B. A., "Solubility Polytherm for the System CO(NH).sub.2 --H.sub.3 PO.sub.4 --H.sub.2 O," Zhur. Prik. Khim. 46 (11), 2405-8 (1973).].
Likewise, the three-component system of CO(NH.sub.2).sub.2 --NO.sub.3 --H.sub.2 O was studied in considerable detail by Sokolov, V. A., "The Equilibrium in the System Urea-Ammonium Nitrate-Water," J. Gen. Chem. (USSR) 9, 753-8 (1939). Kummel determined the solubility concentration in the system CO(NH).sub.2 --H.sup.+ --NH.sub.4.sup.+ --NO.sub.3.sup.- --PO.sub.4.sup.3- --H.sub.2 O and defined many invariant points, but did not provide solubility data between the invariant points which are necessary to predict solution fertilizer compositions [Kummel, R., "Crystallization Equilibria in the Quinary System at 25.degree. C.," Z. Chemie 17 (12), 454-5 (1977)].
Narkhodzhaev studied the solubility in the system urea-ammonium nitrate-phosphoric acid-water, but his study was limited to only one weight ratio of urea to ammonium nitrate, i.e., (45:55) [Narkhodzhaev, A. K., Takhtaev, S., Nabier, M. N., "Study of Solubility in Urea-Ammonium Nitrate-Phosphoric Acid-Water System"].
Other researchers who studied the solubility of urea and phosphoric acid are as follows:
Kaganski, L. M., Babenko, A. M., "Solubility in the Quaterary System Urea-Ammonium Nitrate-Monoammonium Phosphate Water," Zhur. Prik. Khim 43 (4), 742-9 (1970).
Kaganski, L. M., Babenko, A. M., "Study of Solubility in the System NH.sub.4 H.sub.2 PO.sub.4 --(NH.sub.4).sub.2 HPO.sub.4 --CO(NH.sub.2).sub.2 --H.sub.2 O," Zhur. Prik. Khim. 403 (11), 2421-5 (1970).
Willard, J. W., et al., "Solubility in the System CO(NH.sub.2).sub.2 --H.sub.3 PO.sub.4 --NH.sub.3 --H.sub.2 O at 0.degree., 25.degree., and 50.degree. C.," J. Chem. Eng. Data 29 (1), 52-4 (1984).
More recently, researchers have produced solutions from urea reacted with phosphoric acid or combinations of phosphoric acid and sulfuric acid, see U.S. Pat. No. 4,315,763, Stoller, Feb. 16, 1982, and U.S. Pat. No. 4,461,913, Lewis, et al., July 24, 1984, assigned to the assignee of the present invention. These products, however, do not contain the desirable component, nitrate nitrogen. Although crops do absorb some ammonium nitrogen, they more readily absorb most of their nitrogen requirements as nitrate nitrogen. It is, of course, appreciated that microorganisms in the soil nitrify ammonia nitrogen and convert it to nitrate nitrogen; however, the conversion reaction can require considerable amounts of time, thereby resulting in some loss of ammonia nitrogen to the vapor state. Thusly, there are distinct advantages in having nitrogen in the nitrate form for immediate growth response and reduction of ammonia losses.
A still more recent development in this prior art is taught in U.S. Pat. No. 4,531,962, Achorn, et al., July 30, 1985, assigned to the assignee of the present invention, wherein urea-ammonium nitrate solution and urea are reacted with phosphoric or sulfuric acid to produce acid-type fertilizer solutions. However, Achorn, et al.'s, study was limited to a rather small range of weight ratio CO(NH.sub.2).sub.2 --N:NH.sub.4 NO.sub.3 --N. Their teachings indicate that the most promising products have such a weight ratio in the range of from 1.875 to 2.625. It has long been presumed that Achorn, et al., confined their study to this narrow range of ratios of urea-N to ammonium nitrate-N because of the lower solubility of the nitrate component as compared to the solubility of urea. However, it has now been discovered in the investigations leading to the instant invention that when urea is added along with the conventional urea-ammonium nitrate solution (32 percent nitrogen) as the starting material, quite unexpectantly, the resulting solution can contain a TPN (N+P.sub.2 O.sub.5 +K.sub.2 O) of 35 percent or more at 0.degree. C. by increasing the phosphoric acid input along with the increased input of urea.
Accordingly, it has now been found that a novel method can be utilized to produce high-analysis acidic-type fertilizer solutions by reacting urea-ammonium nitrate solutions with phosphoric acid and urea to provide a desirable wide range of urea-N to ammonium nitrate-N weight ratios of 15 to 4.
The chemical mechanisms effected in the practice of the teaching of Achorn, et al., result in the precipitation of CO(NH.sub.2).sub.2.HNO.sub.3 and NH.sub.4 H.sub.2 PO.sub.4, whereas the mechanisms utilized in the practice of the instant invention are quite different from those taught by Achorn, et al. For example, the phosphate utilization in the present invention invites reaction with the ammonium ions derived from the ammonium nitrate to thereby form monoammonium phosphate, while at the same time it reacts with the urea constituent to form a resulting urea phosphoric acid adduct compound at relatively moderate phosphate concentrations.